Potable (i.e., drinkable) water is a necessity to which millions of people throughout the world have limited access. Water is often considered to be the most basic and accessible element of life, and seemingly the most plentiful. In every liter of water in rivers or lakes, fifty more lie buried in vast aquifers beneath the surface of the earth. There is no standard for the quantity of water a person needs each day but experts often place the minimum at 100 liters for adults. Most people drink one or two liters, with the rest typically being used for cooking, bathing, and sanitation. Adult Americans consume between 400 and 600 liters of water each day.
The population of earth continues to expand. If water were spread evenly across the globe, it is likely that there would be a sufficient quantity to satisfy the needs of everyone. However, rain falls inequitably with respect to both time and geographical location. Delhi receives fewer than forty days of rain each year, all in less than four months. In other Indian cities, the situation is worse. Nevertheless, the country must sustain nearly twenty percent of the earth's population with four percent of its water. China has less water than Canada, but contains forty times as many people.
In addition to receiving a majority of its rainfall over the span of only a few months, most of the people of Indian reside in hardrock areas, where underground water is difficult to reach. The problems became known worldwide in the 1960s, when a series of severe droughts throughout India resulted in a large number of deaths. In response, the United Nations provided drilling equipment that greatly expanded the number of boreholes through the hardrock to the underline groundwater. Even with the significant increase in the number of boreholes, the goal of making water an accessible commodity for the Indian people was problematic, since the number and the quality of the available hand pumps were inadequate. Most of the hand pumps in India in the 1960s and the early 1970s were poor-quality cast-iron replicas of European and American pumps that were not designed for use by an entire community. What were needed were VLOM (Village Level Operation and Maintenance) pumps for use in areas in which electrical power is not readily available. As indicated by its name, a VLOM is intended for use by a number of people and should be maintainable by a local mechanic.
In 1975, UNICEF (United Nations International Children's Emergency Fund), along with the Indian government, identified the Sholapur pump as the hand pump which would be modified for the purpose of facilitating mass production and local upkeep. The modified hand pump is referred to as the “India Mark II.” The design is non-proprietary, includes standardized specifications and replacement parts, and is formed of steel, rather than cast iron.
A representation of the India Mark II as shown in FIG. 1. The hand pump 120 includes a handle 122 that is pivotally connected within a head 124. A removable cover 126 allows access to mechanical components within the head, so that repairs may be made when necessary. A stand assembly 128 includes three legs 130, but only two are shown in FIG. 1. Typically, the stand assembly is at least partially buried following installation of the hand pump. A water tank 132 leads to the outlet 134 of the hand pump. Buried components, such as the cylinder assembly and plunger rod are not illustrated. When a person pumps the handle 122 upwardly and downwardly, water is drawn through a well casing 136 to the water tank 132 and is released through the outlet. Mass production of the India Mark II started in 1977 at an annual rate of 7,200. According to UNICEF information, by 1984, 36 manufacturers were producing 100,000 pumps per year, with the annual production increasing to 200,000 by 1987. It is estimated that approximately 50,000 new pumps are installed in India each year. Moreover, the India Mark II has been exported to countries in Africa and Latin America and has been viewed as the answer to a decentralized water system. The hand pump remains relatively the same, but upgrades to the Mark III and Mark IV are available.
The availability of the India Mark II and other hand pumps has greatly improved conditions within India and other regions of the world. However, producing water that is sufficiently pure for human consumption remains as a major concern. It is not possible to determine from its appearance whether pump-acquired water is safe to drink. Simple procedures, such as boiling or use of a household charcoal filter, are not sufficient for treating water from an unknown source. Even natural spring water should be tested before determining what type of treatment is needed. Brackish water is water that has up to 2,000-5,000 ppm (parts per million) total dissolved solids (TDS). “Mildly” brackish water has a TDS of about 500-1,000 ppm. Drinking water specifications (IS:10500-1191) include identifications of both the recommended and “acceptable” levels: a TDS of 500 ppm (up to 2,000 ppm, if no other source is available); 0.3 ppm iron (up to 1.0 ppm); 1.0 ppm fluoride (up to 1.5 ppm); 0.05 ppm arsenic; 0.03 ppm aluminum (up to 0.2 ppm); with a ph of 6.5-8.5.
There is no source of water which is considered inherently “safe” for drinking. Deep groundwater is generally of high bacteriological quality (i.e., a low concentration of pathogenic bacteria, such as campylobacter or the pathogenic protozoa Cryptosporidiumand Giardia), but may be rich in dissolved solids, especially carbonates and sulfates of calcium and magnesium. In comparison, the bacteriological quality of shallow groundwater varies significantly. Arsenic contamination of shallow groundwater is a serious problem in some areas, notably Bangladesh and West Bengal in the Ganges Delta. Fluoride is also a potentially dangerous contaminant, possibly leading to Flourosis, a serious bone disease.
Water which is acquired using a pump or other means should then be purified. There are known processes for water purification. The selection among the processes is based upon the particular contaminants present in a water supply. Ultrafiltration membranes use polymer films with chemically formed microscopic pores that can be used in place of granular media to filter water effectively without coagulants. The type of membrane media determines how much pressure is needed to drive the water through the media and determines the size of micro-organisms which are filtered by the media. In ultrafiltration, ultrastatic pressure forces a liquid against a semi-permeable membrane. Suspended solids and solutes of high molecular weight are retained up to about 0.01 microns in size. This removes bacteria and many viruses, but not salts (ions), while water and low molecular weight solutes pass through the membrane.
Another membrane technology for water purification is reverse osmosis. Reverse osmosis is the process of pushing a solution through a filter that traps the solute on one side and allows the pure solvent to be obtained from the other side. A reverse osmosis membrane is semipermeable, meaning it allows the passage of solvent but not solute, down to a particle size of approximately 0.0005 microns, which is sufficient to remove viruses and salts (ions). The membranes used for reverse osmosis have no pores. Rather, the separation takes place in a dense polymer layer of only microscopic thickness. Water goes into solution in the polymer of which the membrane is manufactured, and crosses the polymer by diffusion. This process normally requires a high pressure to be exerted on the high concentration side of the membrane, usually 4-14 bar (60-200 pounds per square inch (psi)) for fresh and brackish water and 40-70 bar (600-1,000 psi) for salt water, which has approximately 24 bar (350 psi) natural osmodic pressure that must be overcome.
Thus, there are a number of interrelated problems with providing human consumable water. The first issue is providing access to a water source. The India Mark II has been instrumental in addressing this first issue. Then, issues arise regarding purification. In the developing regions in which the India Mark II is most beneficial and in regions in which a natural disaster has occurred, there may be no power source available to produce the pressure necessary for reliable filtration. There are commercially available hand pumps which generate sufficient pressure, but for a community-shared India Mark II, the time requirements and the expense of a second, slower functioning pump may dictate against this second shared pump.